Wireless telecommunication services are today offered to a large fraction of the world's population. To this end, access networks have been installed, which allow an end user equipped with a terminal device for wireless communication making use of voice and data communication with other end users throughout the world. The currently most widespread technology standard used for wireless communication is the global system for mobile communication, short GSM.
In the following, the GSM architecture will be shortly summarized with reference to FIG. 1. FIG. 1 shows the essential components of a GSM public land mobile network (PLMN) 10 serving terminal devices TD1, TD2 and TD3. The terminal devices TD1 and TD2 are located in a first network cell 12 formed by the radio area coverage of the first base transceiver station (BTS) 14. A second and third BTS 16 and 18 cover second and third network cells 20 and 22. As can be seen from FIG. 1, several BTSs together are controlled by one base station controller (BSC) 24. Similarly, a second BSC 26 controls the first transceiver station 14. The combined traffic of terminal devices TD1 to TD3 in their respective network cells is routed through a mobile switching center MSC 28. Connections originating from or terminating in a fixed network such as a public switched telephone network (PSTN) or an integrated services data network (ISDN) are handled by a gateway mobile switching center (GMSC) 30.
The MSC 28 is connected to a number of databases for call control and network management. A home location register (HLR) 32 stores permanent data such as a user profile for users registered with a network operator. The HLR is accessed first, when a user's current location has to be determined in the case of a call. A visitor location register (VLR) 34 stores the data of users who are currently in a certain area. The VLR may also assign and store local data's such as a temporary identification. An authentication (AUC) 36 generates and stores security-related data such as keys used for authentication and encryption. An equipment identity register (EIR) 38 registers equipment data.
The base transceiver stations and the base station controllers for a base station subsystem of a GSM radio access network. The MSC, GMSC, HLR and VLR form components of a switching and management subsystem (SMSS).
Next, the functionality of a MSC is explained in more detail. The MSC forms a switching node of a GSM PLMN. In addition to providing all functionalities known from a switching node of a PSTN, an MSC further assigns and manages wireless resources and the mobility of terminal devices. Therefore, an MSC registers the current location of terminal devices and provides handover functionality for continued communication during the change of a terminal device from one network cell to another.
In establishing a call between terminal devices TD1 and TD2 located within identical network cells according to the GSM standard, both control data used for establishing the connection and user data, which form the actual user information to be transferred between the terminal devices, are routed from an originating terminal device, say TD1 to the BTS 14, BSC 26 and MSC 28, and back from MSC 28 to BSC 26, BTS 14 and TD2. The term control data is used herein with a general meaning to include both control requests or commands and control parameters related to a request or a command.
WO 2004/002177, which is incorporated herein by reference in its entirety, describes a method, in which the transmission path just described for a regular call between terminal devices can be switched to a shorter path for the transmitted user data, which involves only the base station subsystem (BSS) and does not access a core network.
The proliferation of wireless access networks typically ends in regions, where the majority of the population cannot afford to use wireless telecommunication services offered at a cost, which at least compensates the capital expenditure for installing and operating the access network. For this reason, wireless telecommunication services are not widely available in rural areas with a population that has too small an income to justify the investment of installing and operating a wireless access network.
Prototype systems are being given a trial in various markets, which provide wireless access through wireless local area networks based on IEEE 802.11 standards. Voice calls are enabled by using a voice-over-internet-protocol (VoIP)-technology. However, providing mobile coverage for rural environments is not economically feasible with this solution due to the dispersed population in rural areas and the low area coverage per access point. Efforts are being made to increase the area coverage and the transmission speed. However, the ability of the corresponding technologies based on IEEE 802.11 standards to provide high-speed access and large area coverage implies high power requirements and a higher cost for the chipset, which translates into higher overall system costs for a feature, which in the market under consideration is not of much relevance. For a rural market, low power consumption for both mobile devices and network nodes is an important requirement.